Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

SM465 Vs SM420...?

Discussion in 'The Garage' started by Chevy409, Aug 5, 2002.

  1. Chevy409

    Chevy409 Registered Member

    Joined:
    Mar 5, 2001
    Posts:
    81
    Likes Received:
    0
    I'm running a SM465 right now and love it off-road but on road, it's not much fun. The spread between 2nd and 3rd and 3rd and 4th is just too much if you're going to "hotrod" around town or something like that. Now, I've never ran a SM420 but the two trannies look nearly identical (cast iron, gears no chain, 4-speed) and I've heard the SM420 even holds up better, but how's the stretch between gears? Does it feel better than a SM465? Is first gear lower or higher? Any recommendations or info is much appreciated, thanks. /forums/images/icons/confused.gif
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,173
    Likes Received:
    1,384
    Location:
    E-town baby!
    The 420 is no stronger than a 465. The only real differences are that first gear in a 420 is 7.05:1 and the 465 is 6.55:1. The 420 is a shorter overall length which makes em popular with the Heep crowd.
    To get a strong granny low manual with better on road ratio's you need a NV5600 6 speed. Even the NV4500 has wide ratio's, it just adds a .73:1 overdrive for 5th.

    What axle ratio's are you running? Really tall gears with a 465 makes the problem even worse...

    Rene
     
  3. BigOrange90Jimmy

    BigOrange90Jimmy 1/2 ton status Premium Member

    Joined:
    May 24, 2002
    Posts:
    2,923
    Likes Received:
    0
    Location:
    Wilmington, NC
    Not much difference in the gear ratios between the two, with the exception of the First gear in the 420 being 7.06:1. It has a lower torque rating than the 465, but it seems to hold up better. Other than that, just a major lack of parts for the 420 is really the only downside.
     
  4. Chevy409

    Chevy409 Registered Member

    Joined:
    Mar 5, 2001
    Posts:
    81
    Likes Received:
    0
    I'm running 3.08's with 33's so that's probably adding to the problem. Will the 5 and 6-speeds hold up to big block strength and the duties of off-roading? I'd love to get one though. Trannies like the NV4500, are they hard to come by?

    Thanks everyone
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,173
    Likes Received:
    1,384
    Location:
    E-town baby!
    Both the NV4500 and NV5600 are as strong or stronger than the SM465. They are both relatively new tranny's though so they are expensive and can be hard to find. The NV4500 is much easier and less spendy because it's been around longer. The NV5600 has only been out for 2 or 3 years and it's a real monster.

    I'd swap to 3.73's or 4.10's if I were you. It'll help your motor stay in it's power band better. I run 36's with 3.73's and the SM465 and the split between any of the gears is liveable. 4.10's would probably be better...

    Rene
     
  6. chulisohombre

    chulisohombre 1/2 ton status

    Joined:
    Apr 11, 2002
    Posts:
    4,141
    Likes Received:
    14
    Location:
    Bangor,Pa
    mines 3.73 for now,but i had 4.10 gears before i blew up my last 12 bolt.now i bought 14ff with 4.10 so i will have my gears back and can finally run 4 wheel drive again.you will see a major power gain from changing gears.i just wish i hadnt blown out the last rear end i had.whoever changed the gears didnt torqe the ring gear bolts good enuf and the whole case grenaded.so i got stuck with stock 3.73 axle that i found just to get it on the road.keep the 465 and change your gears.you'll never regret it.
     
  7. BLUESMAN

    BLUESMAN 1/2 ton status

    Joined:
    Oct 3, 2001
    Posts:
    951
    Likes Received:
    1
    Location:
    Phoenix(but it\'s a dry heat...like an oven!)AZ.
    It's your diff. gears that is killing you!I run the SM465 trans(had an TH350...SUCKED),with 4.10 geared 3/4 ton diffs and 38" tires.The truck is a screamer in town and damn good rock crawling(it has the 2.62 geared 208 T-case).Change you diff gears and you love your SM465 trans again.Mike
     
  8. Chevy409

    Chevy409 Registered Member

    Joined:
    Mar 5, 2001
    Posts:
    81
    Likes Received:
    0
    /forums/images/icons/smirk.gif All right, cool. Thanks for all the input guys. I knew my gears were screwing me over but i didn't think that's why my tranny's spreads are so far apart, makes sense though. I'm leaning towards changing the rears but there's still one thing that worries me: What about interstate speeds? I have to get up to about 2500 RPM to get close to 70 MPH right now so will I have to be cranking with something like 3.73's? Is there a medium gear like 3.42's or something? thanks again.

    Hey Bluesman, least that's one thing I already know, oughta-smack-it's suck. I got a TH350 in one of my blazers right now, can't stand the thing.
     
  9. bigjbear

    bigjbear 1 ton status Staff Member Moderator

    Joined:
    Feb 18, 2000
    Posts:
    13,971
    Likes Received:
    451
    Location:
    Marietta GA
    What size tires are you running? I've got 35s & 4.56s and it will booggy down the hiway at 75MPH no problem. Thats with a crappy TH350, you will have a true 1:1 ratio in 4th, unlike the non-lock up autos. Chevy liked to gear trucks way too high.
     
  10. Chevy409

    Chevy409 Registered Member

    Joined:
    Mar 5, 2001
    Posts:
    81
    Likes Received:
    0
    I've only got 33's so with the low geared SM465 and high 3.08's, things evened out ok and it doesn't feel that bad. Majority vote sounds like the gears gotta go. Still not positive though.
     
  11. BigOrange90Jimmy

    BigOrange90Jimmy 1/2 ton status Premium Member

    Joined:
    May 24, 2002
    Posts:
    2,923
    Likes Received:
    0
    Location:
    Wilmington, NC
    Yes they make a 3.42. Mine came from the factory with that ratio and a Gov-Loc. WANT IT?! /forums/images/icons/smile.gif I'll sell you the whole darn axle.
     
  12. bigjbear

    bigjbear 1 ton status Staff Member Moderator

    Joined:
    Feb 18, 2000
    Posts:
    13,971
    Likes Received:
    451
    Location:
    Marietta GA
    I reread after i posted, sorry about that. If your 33s are 33" tall AND you plan on staying w/ that size I'd go w/ 4.10s.
     
  13. BLUESMAN

    BLUESMAN 1/2 ton status

    Joined:
    Oct 3, 2001
    Posts:
    951
    Likes Received:
    1
    Location:
    Phoenix(but it\'s a dry heat...like an oven!)AZ.
    4.10's are going to be kinda low for your 33" tires.Unless you are planning on going to 35's( and who does'nt?)I would go with 3.73's.I can't even use 1st(granny) gear on the street.Heck the truck only goes like 2mph in 1st and 4lo at idle.I've seen a guy who was running 33's with 3.08 gears use 1st gear...must be a dog at highway speeds!Change your gears or go to 3/4 ton diffs and get the gears and the diffs at the same time.Mike
     
  14. bigjbear

    bigjbear 1 ton status Staff Member Moderator

    Joined:
    Feb 18, 2000
    Posts:
    13,971
    Likes Received:
    451
    Location:
    Marietta GA
    3.73s & 33s sounds too high to me. SBCs will go above 1700 RPM if you let them, 3500 is no worries-if you can afford the gas.
     
  15. Chevy409

    Chevy409 Registered Member

    Joined:
    Mar 5, 2001
    Posts:
    81
    Likes Received:
    0
    A few things i probably should've said from the beginning:
    I already have 3/4 diffs, a 12 bolt and dana 44 and my engine is a 1965 big block 409, about 8 to 9 MPG and I love every mile I get /forums/images/icons/wink.gif
    Right now, the truck does great on highways. The big block has more nut than needed to lug along in 4th gear so higher RPM's aren't really essential. 3.73's are most likely what i should get but since I'm near happy with sh@tty 3.08's I think I'll settle for something in the middle, like 3.42's. Hey BigOrange, do you have the front diff too and how much just for the gears? I'm a highschool kid with an empty pocket but a yard full of stuff, can I trade you something?
    Thanks for being patient with me everyone. /forums/images/icons/tongue.gif
     
  16. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,173
    Likes Received:
    1,384
    Location:
    E-town baby!
    A 12 bolt and Dana 44 are 1/2 ton axles...

    Rene
     
  17. chulisohombre

    chulisohombre 1/2 ton status

    Joined:
    Apr 11, 2002
    Posts:
    4,141
    Likes Received:
    14
    Location:
    Bangor,Pa
    you beet me to it.12 bolt and d44 are only 1/2 ton unless you do 8 lug conversion on the front d44,but it still has the same strength as the 1/2 ton with 8 lug hubs to make it 3/4 ton.someday i will get my 1 ton dana 60 and i will be set. /forums/images/icons/laugh.gif .need cash for that though.haha
     
  18. TopOff

    TopOff 1/2 ton status

    Joined:
    Jan 16, 2002
    Posts:
    1,760
    Likes Received:
    0
    Location:
    Folsom, ca
    According to 4lo.com's gear calculator if you have 35" tires, 4.56 gears and a 1:1 final drive you will be "bogging" around 3064.3 RPMS going 70 MPH. If you have a torque converter you can probably add another 250 rpms to that.

    I just swapped out my th350 with 3.73s and 35" BFGs really 34.75" tire diameter. I was pulling 2500 rpms at 65mph.

    I LOVE my 3.73s with 35" tires. I am thinking of getting some 36" and keeping my gears.

    I now have the sm465 and I run 2500 rpms at 70 mphs. This affords me ~15 MPG.
    It's a good thing I got the doubler to help with off-road gearing.
     
  19. Chevy409

    Chevy409 Registered Member

    Joined:
    Mar 5, 2001
    Posts:
    81
    Likes Received:
    0
    So what are ten bolt axles (besides junk)? I thought those were half tons and I do realize the axles are the same in the 12 bolt and dana 44 but isn't there at least some difference? Anyway, I have one last question. I know some guys on the borad have done the NV4500 swap and I was just wondering what kind of work this is asking for. Tough job or a bolt in? /forums/images/icons/frown.gif
     
  20. TopOff

    TopOff 1/2 ton status

    Joined:
    Jan 16, 2002
    Posts:
    1,760
    Likes Received:
    0
    Location:
    Folsom, ca
    You should click on REPLY to the specific person to whom you are addressing. This way, that person (if setup) will get an email that someone has replied... as I recieved.

    I don't think the 10 bolts (fronts) are "junk", as that is what I have in my blazer (30 spline). I have been rockin' it for the last four years, and have yet to break something. Depends on the trail, and your driving style.
     

Share This Page